Cathode ray tube



March 7, 1967 SHRADER 3,308,327

CATHODE RAY-TUBE Filed June 12, 1964 I 2 Sheets-Sheet l INVENTOR. 7 7276?) Mia 010M peripheral side wall portion.

3,308,327 CATHODE RAY TUBE Terry M. Shrader, Leacock, Pa., assignor to Radio Corporation of America, a corporation of Delaware Filed June 12, 1964, Ser. No. 374,755 2 Claims. (Cl. 31364) This invention relates to cathode ray tubes, such as the shadow mask color cathode ray tube, which have an electrode, e.g. the shadow mask electrode, removably mounted adjacent to the phosphor screen of the tube. The invention is particularly directed to means for mounting such electrodes.

It is an object of this invention to provide novel means for removably mounting such an electrode with improved accuracy of its position.

Another object of the invention is to provide novel means for removably mounting such an electrode so the electrode can be mounted on and removed from its supports a number of times during manufacture of the tube and be reseated in precisely the same position each time.

Another object of the invention is to provide novel mounting means for such an electrode which reduces undesirable electrode movements when the electrode becomes heated and thermally expands during tube operation.

Another object of the invention is to provide novel mounting means for such an electrode which simplifies fabrication of the cathode ray tube.

A cathode ray tube in which the invention can be used, comprises an envelope including a faceplate panel having a generally rectangular faceplate portion and a The faceplate is disposed centrally perpendicular to a central tube axis and has major and minor surface bisecting axes. The interior surface of the side wall is tapered relative to the central tube axis. A phosphor screen is disposed on the faceplate, and electron gun means are provided for projecting electrons toward the screen. A plurality of electrode support studs are attached to the tapered surface of the panel side wall and include frustoconical tips which are perpendicular to the tapered surface and which project inwardly toward the central tube axis. An electrode, e.g., a multi-apertured shadow mask electrode is disposed substantially parallel to and coextensive with the color phosphor screen. The electrode comprises a generally rectangular frame having an apertured member or mask mounted thereacross. A plurality of leaf spring support straps are provided which have one end thereof attached to the frame and the other end provided with an aperture into which the support studs are received for supporting the electrode in its intended position.

In accordance with the invention, each of the support straps has a face of its apertured end disposed substantially parallel (e.g. by a suitable bending of the strap) to the tapered side wall surface. Each support strap includes three contact elements which project into the strap aperture. In a preferred form, the contact elements have arcnate ends whose radius of curvature substantially matches that of a portion of the frustoconical stud. The transverse end faces of the contact elements are angled (e.g. by a suitable bending of the elements or a grinding of the end faces) relative to the central axis of the aperture. Thus when the support straps are disposed over the studs, the trailing edges of the end faces contact the studs thereby preventing the leading edges from gouging the studs.

As used herein transverse end face (or end face) is the end surface of a strap-like contact element which is provided by the thickness dimension of the contact element and which faces the center of the strap aperture.

In the drawings:

nited States Patent C) 3,308,327 Patented Mar. 7, 1967 FIG. 1 is a side elevation view partly in section of a cathode ray tube embodying the invention;

FIG. 2 is a section of the cathode ray tube of FIG. 1 taken along line 2-2 thereof;

FIGS. 3 and 4 are top plan and side elevation views, respectively, of the leaf spring support strap of the tube of FIG. 1;

FIG. 5 is an enlarged elevation view partly in section of the apertured portion of the support strap disposed over the support stud;

FIG. 6 is a section taken along line 66 of FIG. 5;

FIGS. 7, 8, and 9 are enlarged plan views of alternative aperture and contact element designs of the sup port strap of FIGS. 3 and 4; and

FIG. 10 is a plan view of a modification of the support strap of FIGS. 3 and 4.

Referring to FIGS. 1 and 2, a cathode ray tube 10 includes an envelope 12 having a shallow bow-like faceplate panel 14- which is disposed centrally and perpendicularly to a central axis AA of the cathode ray tube 10. The faceplate panel 14 is sealed along the rim 15 at its open end to the open end of a funnel portion 16 of the envelope 12 by a frit ring seal 18. The faceplate panel 14 includes a generally rectangular, curved, faceplate portion 20 and a peripheral side wall portion 22. The faceplate 20 has perpendicular bisecting major and minor axes xx and yy which are perpendicular to and intersect the tube axis AA. The internal surface 24 of the side wall 22 is tapered with respect to the central tube axis AA in an outward flare away from the faceplate 20 toward the rim 15 A mosaic luminescent screen 26 comprising a multiplicity of elemental dot-like deposits of different color emitting phosphors is disposed on the internal surface of the faceplate portion 20. The screen 26 may be aluminized according to known techniques.

A multi-apertured shadow mask electrode 28 is disposed adjacent to and substantially co-extensive with the faceplate 20 and the mosaic phosphor screen 26. The shadow mask electrode 28 comprises a multi-apertured sheet metal member 30 mounted across a generally rectangular frame member 32. The frame 32 is of generally L-shaped cross-section (FIG. 1) with one flange 34 of the frame substantially parallel to the central tube axis AA. In the drawing, the apertured member 30 and the frame 32 are shown of approximately equal thickness for purposes of clarity. In practice, the frame 32 is many times thicker than the apertured member 30.

Four electrode support studs 36 are secured to the tapered surface 24 of the panel side wall 22 at locations nearly midway between the four corners thereof. Each of the studs 36 includes a frustoconical tip 38 which is axially perpendicular to the tapered surface 24 fiom which it projects. The tip 38 project inwardly toward the center of the tube 10.

Each of a plurality of leaf spring support straps 40 is fixed at one end thereof to the flange 34 of the shadow mask electrode frame 32. Each of the support straps 40 is provided with a suitable aperture near its other (free) end into which the frustoconical tips 38 of the support studs 36 are received so as to support the shadow mask eletcrode 28 within the panel 14. The spring support straps 40 are such that their apertured free ends may be depressed toward the frame 32 under further tension so as to mount the shadow mask electrode 28 onto the studs 36 and to remove it therefrom. Such removable mounting of the mask electrode 28 is useful because the mask electrode 28 may be removed during the deposition of the mosaic phosphor screen 26 in accordance with known screening practices.

Referring to FIGS. 3 and 4, each of the leaf spring support straps 40 is bent along a line 42 near the mid point of the strap to provide a free end portion 44 having an aperture 46 into which a support stud 36 is received and a support portion 48 which is secured such as by welding to the flange 34 of the electrode frame 32. The bend line 42 of the strap 46 (see FIG. 3 for example) is made at an acute angle with the long edge 56 of the strap so that when the support portion 48 of the strap is secured flush to the frame flange 34, the flat faces of the free end portion 44 will be slightly tilted with respect to the frame flange 34 and to the central tube axis AA. The angle of the bend line 42 is such that the free end portion 44 has its major surfaces or flat faces disposed substantially parallel to the tapered surface 24 of the panel side wall 22. Thus the conical tip 38 of the support stud 36 is received substantially normal to the flat faces of the free end portion 44 of the support strap 40.

By providing the bend line 42 at an angle so as to tilt the free end portion 44 of the support strap 48, it is possible to use a support stud 36 which is axially symmetrical with respect to its own axis, thus simplifying the attachment of the support studs 36 to the panel side wall 22. In the absence of a tilt to the apertured portion of the support strap, the support stud must be provided with a base which is angled with respect to the axis of the stud so as to provide a perpendicular relationship between the stud and the apertured portion of the support strap. Such a design necessitates an orientation of the stud when it is secured to the panel side wall 22.

Referring to FIGS. and 6, each support strap 48 includes a plurality, e.g. three, stud-contacting faces 52 which face inwardly of the aperture 46. The stud-contacting faces 52 are preferably provided as the transverse end faces of three support fingers 54 which project inwardly into the aperture 46. The end faces 52 are at an angle 5 relative to the common central axis BB of the strap aperture 46 and the stud 36. Such angle is preferably provided by bending the support fingers 54 slightly out of the plane of the support strap 40. Alternatively, the end faces 52 may be ground to provide the desired angle [3. In either event, the angle 5 is made to be equal to or preferably slightly greater than the angle of taper a of the frustoconical stud tip 38. For example, the angles at and B may be 12 and 15 respectively. Thus when the support strap 48 is disposed over the stud tip 38, the trailing edge 56 of the end face 52 (as opposed to the leading edge 58 thereof) contacts the stud tip 38. Therefore, as the support strap 46 is pressed tightly down on the stud tip 38, the strap fingers 54 do not gouge the tip 38. When the support strap 40 is reseated on the stud tip 38 a number of time as is normal practice in the manufacture of the cathode ray tube, the stud tip 38 is not deformed to an extent that prevents the support strap 40 from reseating in precisely the same location as it was first seated.

The contact made by the end faces 52 may be by the trailing edges 56 alone or by the entire surfaces of the faces 52 including the leading edges 58. A contact involving the entire surfaces of the end faces 52 (including the leading edges 58) will result in those cases where the angles a and [i are equal. The important consideration is that angle 5 not be smaller than angle a (as in the prior art) whereby the leading edges 58 alone would contact the stud. Should such a condition exist, gouging of the stud and inaccurate reseating of the support strap 40 on the stud would result.

Where contact is described herein as being by the trailing edge 56 alone, such contact would necessarily involve some finite portion of the surface of the end faces 52. It is therefore intended that reference to trailing edge contact alone, not preclude contact by some finite portion of the end face surface.

In order to further reduce possible distortion of the stud tip 38 by the faces 52, the faces 52 are provided with an arcuate contour. The contour is of a magnitude which substantially matches the arcuate contour of the stud tip 38 at the location therealong where the faces 52 contact it.

Although a support strap 40 is preferred which has an d aperture with fingers 54 as illusrtated in FIGS. 5 and 6, other aperture designs may be provided for the support strap. FIGS. 7, 8, and 9 illustrate other suitable aperture designs.

In FIG. 7, an aperture 60 is provided which is substantially triangular. The three stud-contacting surfaces 62 thereof are tapered as desired either by a coining of the aperture 60 or by a suitable grinding of the thickness faces 62 of the aperture.

In FIG. 8, a generally triangular aperture 64 is provided wherein the support strap is cut away with slots 66 at the corners of the aperture. The stud-contacting thickness faces 68 of the aperture 64 may be tapered either by coining or grinding or by bending the portions of the strap adjacent to the stud contacting faces 68. Such bending may be similar to that of the support fingers 54 as illustrated in FIGS. 5 and 6.

In FIG. 9, a generally circular aperture 76 is provided which includes inwardly projecting support fingers '72 similar to the fingers 54 of FIGS. 5 and 6. The support fingers 72 have substantially straight stud-contacting end faces 74. The stud contacting end faces 74 are tapered, for example, by bending the fingers 72 or grinding the end faces 74 to the desired taper.

In a preferred embodiment of the cathode ray tube 10, the shadow mask electrode frame 32 is curved to substantially conform to the curvature of the faceplate 26 at the periphery thereof. The rim 15 of the faceplate panel 14 is, however, flat. That is, the rim 15 lies in a plane perpendicular to the central tube axis AA. Because of the curvature of the electrode frame 32 and the planarity of the rim 15, the frame 32 is spaced further from the rim 15 at the mid points '78 of the long sides of the side wall 22 then it is at the mid points of the short sides of the side wall 22.

For some purposes it may be preferred that the four electrode support studs 36, FIGS. 1 and 2, be secured to the side wall 22 at approximately equal distances from the rim 15. Two leaf spring support straps 82 of FIG. 10 may be used together with two straps 46 of FIGS. 3 and 4 to achieve such an equidistant spacing. The support strap 82 is similar to the support strap 40 except that it includes a side tab 84 at the end thereof opposite the end face 44. In attaching the support strap 82 to the electrode frame 32, the tab 84 is disposed along side the frame flange 34 and welded thereto so that the apertured face 44 is disposed at least partially below (as viewed in FIG. 1, on the gun side of) the frame flange 34. Thus, the apertures 46 of the support straps 82 (used on the long sides of the rectangular mask electrode 28) are substantially co-planar with the apertures 4-6 of the support straps 40 (used along the short sides of the mask electrode 28). The disposition of the apertures 46 in substantially the same plane reduces the likelihood of glass fracture due to the stresses in the glass, which are disturbed by the presence of the support studs 36.

Under normal operating conditions, the shalow mask electrode 28 of a shadow mask cathode ray tube becomes hot due to electron bombardment and thermally expands relative to the faceplate panel 14. Such expansion causes a shift of the mask apertures relative to the phosphor dots of the screen 26. If no compensation is made for such shift, an attendant misregister of the electron beam and the phosphor dots results. The proper compensation can most easily be made if the shift of each mask aperture is substantially radial with respect to the center of the mask. The compensation can then be conveniently incorporated in an optical lens used in the photographic deposition of the phosphor screen. An example of a lens used to provide radial correction is described in US. Patent 2,817,27 6 issued to D. W, Epstein, et al. on December 24, 1957.

If the shadow mask electrode 28 were thermally expanded with no constraining forces applied thereto (such as is applied by the spring-stud supports), each point on the mask electrode 28 Would move substantially radially with respect to the center of the electrode. Of the peripheral points on the rectangular mask electrode 28, the four points on the axes xx and yy and the four points at the corners of the electrode would remain opposite the points on the panel 14 to which they were opposite before expansion began.

In order to achieve an expansion of the mask electrode 28 in which each point thereof moves substantially radially, the mask electrode should be supported such that the peripheral points on the axes xx and yy and at the corners of the electrode (rather than some other points) are constrained to remain opposite given panel points throughout the expansion. If other peripheral points on the mask electrode 28 were constrained to remain opposite given panel points throughout the expansion, a rotational shifting (which is difiicult to compensate for), as well as a radial expansion, of the mask would result.

The method used for attaching the studs 36 to the panel 14, may provide another reason for, and advantage of, mounting the mask electrode 28 so that the peripheral points on the axes xx and yy and at the corners are constrained against lateral movement. According to one method of attaching the studs to the panel, a portion of each stud is first coated with a bonding material such as glass frit. Then, using the mask electrode as a jig, the studs are positioned in the panel in contact with the inner surface of the side wall 22. The frit is then softened by heating and then solidified to bond the studs to the side wall. If the solidification of the frit on all studs does not occur simultaneously, and if the mask expands or contracts between the frit solidification of the different studs, then unless the mask electrode 28 is mounted so as to constrain the peripheral mask points on the axes xx and yy and at the corners against lateral movement, the mask electrode may not fit properly on the studs when the mask electrode is removed and replaced during subsequent tube processing.

Because of the difiiculty of securing studs to the panel near its corners, such a mounting arrangement is notpreferred. As hereinafter described, the desired support of the mask electrode 28 is accomplished by an off-setting of the studs 36 and springs 40 or 82 from the axes xx and yy as detailed with reference to FIG. 2. The studs 36 are off-set from the four ends of the axes xx and yy a distance a in the same perimetrical direction (e.g. clockwise as viewed in FIG. 2). The points on the mask frame 32 to which the support straps 40 and 82 are attached are off-set a distance b (which is greater than a) in the same perimetrical direction. In FIG. 2 the distance 0 represents the length of the support strap 40 or 82 from the center of its aperture 46 to its point of attachment to the mask frame 32. Such an off-set arrangement is designed to compensate for the differential tangential expansion of the support straps 4 0 or 8-2, the

glass panel 14, and the mask 32. Such differential expansion occurs because the materials usually used for these tube parts are such that the straps 40 and 82 have the greatest co-efiicient of expansion, the glass panel 14 the lowest co-efiicient of expansion, and the mask frame 32 an intermediate co-efficient of expansion. For example, the support straps 40 and 82 may be made of S4484 stainless steel having a co-efficient of expansion of 16 10- in./in./ C.; the panel 14 may be made of glass having a co-efiicient of expansion of 9.5 X10- in./in./ C.; and the mask frame '32 may be made of cold rolled steel having a co-efiicient of expansion of 13 X 10- in./in./ C.

Whatever materials are selected for the support straps 4i) and 82, the glass panel 14, and the mask frame 32, the off-sets a and b and the strap length c are such that When the cathode ray tube becomes heated during operation, the glass expansion along length a plus the strap expansion along length c is substantially equal to the frame expansion along length b. Thus the peripheral mask points on the axes xx and yy are not shifted tangentially thereby permitting the movement of all mask apertured due to expansion to be substantially radial as desired.

For purposes of facilitating fabrication of the cathode ray tube 10, one or more of the support studs 36 may be off-set a distance slightly different from the theoretical calculated off-set as described above. Thus, when the mask 28 is removed from the faceplate panel 14, re insertion in exactly the same oreintation is assured. Specifically, it will not be possible to reinsert the mask 28 in a rotated orientation thereof. For example, one of the support studs 36 adjacent to the major axis xx may be off-set slightly more than the calculated amount I and the other support stud 36 adjacent to the other end of the major axis xx may be off-set slightly less than the calculated amount.

In one embodiment of the cathode ray tube 10 having a diagonal faceplate dimension of approximately 25 inches and employing materials as described above, the following off-sets are used with success: (a) each of the two studs 36 near the yy axis are off-set inch; (b) one of the studs near the xx axis is off-set W inch and the other stud near the xx axis is off-set inch; (c) the length 0 of each of the four support straps 40, 8-2 from its aperture 46 to its point of attachment to the mask frame 32 is about 1 /2 inches.

What is claimed is:

1. A cathode ray tube comprising:

(a) an envelope including a faceplate panel having a generally rectangular faceplate portion and a peripheral side wall portion, said faceplate portion being disposed perpendicular to a central axis and having major and minor surface-bisecting axes,

(b) a plurality of electrode support studs attached to said panel side wall and extending inwardly from the interior surface thereof,

(0) an electrode disposed adjacent to and substantially co-extensive with said faceplate portion and including a generally rectangular frame, and

(d) a plurality of leaf spring support straps attached at their one ends to said electrode frame, said straps having apertures near their free ends into which said studs are received for supporting said electrode within said envelope,

(e) a pair of said studs and their associated support straps near the opposite ends of one of said bisecting axes being off-set therefrom to so compensate for differential expansions of said side wall, said electrode frame, and said support strap that those portions of said electrode lying adjacent to said one bisecting axis undergo no substantial tangential shift relative to said faceplate due to the heating of said tube during operation thereof.

2. A cathode ray tube comprising:

(a) an envelope including a faceplate panel having a generally rectangular faceplate portion disposed centrally perpendicularly to a central tube axis and having major and minor surface-bisecting axes and a peripheral side wall portion whose interior surface is tapered relative to said central tube axis,

(-b) a plurality of electrode support studs attached to said tapered panel side wall surface, each of said studs having a frustoconical tip which projects inwardly toward said tube axis and whose central axis is perpendicular to said tapered side wall surface,

(0) an electrode spaced from and disposed adjacent to and substantially co-extensive with said faceplate portion, and

(d) a plurality of leaf spring support straps each of which has one end thereof attached to the periphery of said electrode and the other end thereof provided I with an aperture into which one of said studs is receive-d for supporting said electrode within said envelope, each of said spring support straps having the flat faces of its apertured end disposed substantially parallel to the portion of said tapered side wall surface to which the associated one of said studs is attached, said spring suport strap also including three contact elements projecting into said aperture, said elements having arcuate ends whose radius of curvature is substantially equal to that of the conical surface of said stud at some point along said stud and whose transverse end faces are at its aperture and its point of attachment to said electrode and the expansion of said side wall over the oif-set distance of the associated stud is substantially equal to the perimetrical expansion of said electrode over the off-set distance of said one of said straps.

References Cited by the Examiner an angle to the central axis of said aperture such I UNiTED STATES PATENTS that when said spring support straps are disposed 10 over said studs the trailing edges of said contact 1994251 3/1935 Mueller 339*95 n 2,846,608 8/1958 Shrader 31385 elements contact said studs, 2 856 552 10/1958 E 313 85 (e) said studs being attached to said side wall at 3/1959 Y locations perimetrically off-set along said side Wall 2928967 3/1960 g' 313 64 from said bisecting axes, said support straps being 15 8/1960 Kj f 3 attached to said electrode at locations off-set from 3,004182 10/1961 Pfaender 31364 said bisecting axes in the same perimetrical direction as the off-set of said studs, the distances of said oflsets being such that during tube operation the JOHN HUCKERT Prlma'y Exammer' sum of the expansion of one of said straps between 20 AM ES, A sistant Examiner. 

1. A CATHODE RAY TUBE COMPRISING: (A) AN ENVELOPE INCLUDING A FACEPLATE PANEL HAVING A GENERALLY RECTANGULAR FACEPLATE PORTION AND A PERIPHERAL SIDE WALL PORTION, SAID FACEPLATE PORTION BEING DISPOSED PERPENDICULAR TO A CENTRAL AXIS AND HAVING MAJOR AND MINOR SURFACE-BISECTING AXES, (B) A PLURALITY OF ELECTRODE SUPPORT STUDS ATTACHED TO SAID PANEL SIDE WALL AND EXTENDING INWARDLY FROM THE INTERIOR SURFACE THEREOF, (C) AN ELECTRODE DISPOSED ADJACENT TO AND SUBSTANTIALLY CO-EXTENSIVE WITH SAID FACEPLATE PORTION AND INCLUDING A GENERALLY RECTANGULAR FRAME, AND (D) A PLURALITY OF LEAF SPRING SUPPORT STRAPS ATTACHED AT THEIR ONE ENDS TO SAID ELECTRODE FRAME, SAID STRAPS HAVING APERTURES NEAR THEIR FREE ENDS INTO WHICH 